The present invention relates generally to spinning aperture radiometers and methods, and more particularly to spinning strip (partial) aperture imaging radiometers that synthesize equivalent full circular aperture images and detect moving objects from a plurality of rotating strip aperture image, or synthesized image measurements.
To provide high resolution images from space-based platforms, for example, conventional sensor architectures use active control of large, heavy, deployable optical systems. Depending upon the mission requirements and size of the primary mirror, the active control can range from periodic piston and tilt control of primary mirror segments to piston, tilt, figure, and alignment control of all optical elements of the sensor. Full aperture systems with the same resolution as the present invention have a great deal of light gathering capability because of the relatively large aperture areas. However, to place multi-meter diameter apertures into orbit, full aperture systems competing with the present invention require: segmented optical surfaces and folded support structures, if the optical system diameters are larger than the launch vehicle's fairing; complex and potentially high bandwidth adaptive optical techniques, if thin deformable mirrors are used to save weight; and complex piston and pupil matching control, if implemented as a phased array. Therefore, full aperture systems are relatively heavy and have high technical risk when compared to the present invention.
The processors and methods described herein relate to and provide for an improvement to the system capabilities of the closest prior art, referred to herein as SpinAp. The SpinAp system and processing method is described in U.S. Pat. No. 5,243,351, entitled "Full Aperture Image synthesis Using Rotating Strip Aperture Image Measurements", which is assigned to the assignee of the present invention.
SpinAp is a sensor system and data processing method that is capable of synthesizing images having resolution equivalent to a full circular aperture. The equivalent SpinAp synthesized fill circular aperture has a diameter equal to the largest correlation length associated with the strip aperture's geometry. To accurately synthesize an equivalent full aperture image, SpinAp acquires imaging data using the rotating sensor's focal plane detectors at time intervals appropriate for completely measuring the optical system passband of the equivalent full circular aperture. The images are processed by methods described in U.S. Pat. No. 5,243,351.
The commonality of the approaches between the SpinAp system and the system of the present invention (referred to as SpinAp moving object detection) arises from the use of temporally registered strip aperture measurements to synthesize images having resolution equivalent to a full circular aperture. The equivalent SpinAp synthesized full circular aperture has a diameter equal to the largest correlation length associated with the strip aperture's geometry.
To accurately synthesize an equivalent full aperture image, SpinAp acquires imaging data using the rotating sensor's focal plane detectors at time intervals appropriate for completely measuring the optical system passband of the equivalent full circular aperture. The images are processed by methods described in U.S. Pat. No. 5,243,351.
However, a moving object in the instantaneous field of view of any of the individual frames will result in a motion smear signature in the total synthesized image. Detection of the moving object is required to establish object phenomenology, such as, position, size, trajectory, velocity, acceleration, and point of origin. In addition, the detection process is a precursor to applying processors and methods to the acquired data that permit stationary image synthesis of the moving objects. Therefore, a hierarchy of moving object detection processors and methods is described herein. The hierarchy includes spatial, temporal, spatial frequency, and temporal frequency domain detection processors, which may also incorporate multi-spectral background rejection techniques. The present system makes use of the available measurements to detect moving objects in the field of view of the synthesized images, in the field of view of any pair of SpinAp individual frames, in any one of the SpinAp individual frames, or any combination. The same methods may also be applied to transient event detection.
Therefore, it would be an advantage to have modified SpinAp image processing methods that would result in lower payload weight for a given effective synthesized aperture size, while providing capability to detect moving objects in the sensor's field of view. Furthermore, it would also be advantageous to have a system having image processing and moving object detection methods that provide a lower risk, lower cost, lighter weight, and simpler fabrication deployment alternatives to deploying complex, large full circular apertures (or phased array telescopes) requiring complex adaptive optical systems for space based imaging applications.